Getting the Bronco ready for wheeling season, so I am changing the plugs. On the left are the Motorcraft plugs that are in there, and on the right are the Champion Iridium plugs I bought as a replacement.

Why is the firing tip/igniter on the Champion so much smaller? Is that ok? I’m running a ‘93 5.0 w/Mustang EFI if it matters.

New plugs are too long. Bet they will either hit the vales or pistons. But that is what the iridium look like. They work really well and last a long time. Since they are conical seat the threaded body is too long. That's why they'll hit.

What Rob said

Here’s what got me perplexed. I went to my spare parts box I had put together for Baja, and forgot I had purchased a set of NKG plugs. Take a look..threads are the same length as the other new ones. So the quest is, are the new ones correct and the old ones incorrect? Shorter threaded plugs like the ones I took out would still fire the cylinder, correct?

Hey Scott so 1993 5.0 should use a Motor craft ASF4CA plug. stay away from champion plugs for your application they don't work well. Also platinum and Iiridium plugs don't perform well with older ignition systems. Both the champion and NGK plug look to have to long of a reach.

Ok I’ll go grab a set of those. Thanks much!

That is a Motorcraft # if you can't find them happy to get some and send them to you copper core no platinum.

The parts house probably only has the Champion that's why they are pushing you in that direction. I've not had good luck or performance out of champion products.

I don't why I typed Champion earlier..I didn't mean to.. I was searching for Motorcraft asf4ca and got no hits on google. Went to Ford site and that's where I found the Motorcraft SP450A as OE replacement. Autozone, O'reilly and Advance Auto sites show the same (SP450A) for copper Motorcraft plugs for the '93 Mustang w/5.0. Dang..they're just spark plugs! why is everything such a pita on this Bronco? LOL

NAPA shows an Autolite ASP 764 as an OE replacement, its Copper Core. The picture they show looks to be the shorter thread depth, you’d have to swing by and check the thread depth. They also show some plugs that appear to insert into the cylinder deeper as an alternative. I’m fairly sure the 5.0 is a “non-interference” design, so you could run an alternative plug, but if you don’t have a reason to switch I wouldn’t.

From your picture, the plug type looks like it’s performing well.

Well, you won’t get results searching for ASF42CA, but there it is stamped on the plug and the box. All websites and parts stores know them as SP-450A. Weird. Thanks for the help and info!

Looks like you got the right plug. I'm assuming the reach on the plug is the shorter version.